Properties
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Properties
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Click here to read the lecture notes on this topic. Please take the practice quiz below. This is completely anonymous and no records of results are maintained.
If you do not see the quiz above your browser may not support Java Applets. You may wish to download an update for your browser. Matter Matter is defined as anything that occupies space and has mass. Matter can be found in one of three states: solid, liquid, or gaseous. Elements and Compounds An element is a substance that cannot be reduced to a simpler substance by chemical means. Examples of elements are iron, gold, silver, copper, and oxygen. A compound is a chemical combination of elements that can be separated by chemical but not by physical means. Water is a compound which consists of hydrogen and oxygen. Table salt is a compound which consists of sodium and chlorine. Atoms An atom is the smallest particle of an element that retains the characteristics of that element. There are more than 100 known elements, so there are more than 100 different atoms. Thousands of different materials can be made by chemically combining the proper atoms. A molecule is a particle that is the chemical combination of two or more atoms. The oxygen molecule consists of two atoms of oxygen, The hydrogen molecule consists of two atoms of hydrogen. Sugar is a compound composed of atoms of carbon, hydrogen, and oxygen. The subatomic particles which make up atoms are electrons, protons, and neutrons. The electrons, protons, and neutrons of one element are identical to those of any other element. The reason there are different kinds of elements is that the number and the arrangement of electrons and protons within the atom are different for each of the elements. The electron is considered the small negative charge of electricity. The proton has a positive charge of electricity equal and opposite to the charge of the electron. The electron and proton have the same quantity of charge, although the mass of the proton is approximately 1837 times that of the electron. Some atoms have neutral particles called a neutrons. The neutron has a mass approximately equal to that of a proton, but no electrical charge. One popular theory has subatomic particles arranged in a manner similar to a miniature solar system. The protons and neutrons form a heavy nucleus with a positive charge, around which the very light electrons revolve. The number of protons is equal to the number of electrons making the atom neutral in charge. Elements are classified numerically according to their complexity. The atomic number is determined by the number of protons. A hydrogen atom one proton and one electron. A carbon atom has 6 electrons, 6 protons, and 6 neutrons. ENERGY LEVELS The electron in a atom has both mass and motion. An electron has kinetic energy due to its motion. An electron has potential energy due to its position. The total energy determines the radius of the electron orbit. In order for an electron to remain in its orbit, it must neither gain nor lose energy. Light consists of tiny energy packets known as photons. Photons can contain various quantities of energy. The quantity depends on the color of the light involved. Should a photon of sufficient energy collide with an orbital electron, the electron absorbs the photon's energy. The absorbtion of energy by the electron could also be done via heat or by friction. The electron which now has a greater than normal amount of energy jumps to a new orbit farther from the nucleus. Each orbit may be considered to represent one of several energy levels that the electron may attain. An electron cannot exist in the space between energy levels. When an electron has been elevated to an energy level higher than the lowest possible energy level, the atom is said to be in an excited state. The electron does not remain in this excited condition for more than a fraction of a second before it radiates the excess energy and returns to a lower energy orbit. The excess energy may be in the form of a photon or as heat. Shells and Subshells In general electrons reside in groups of orbits called shells. The shells are arranged in steps that correspond to fixed energy levels. Each shell contains a maximum of 2n2. Shells are full or complete with 2 in the K shell, 8 in the L shell, 18 in the M shell, and so on. Each shell can be divied in to as many as four subshells, labeled s, p, d, and f. s is complete with 2 electrons, p with 6 electrons, d with 10 electrons, and f with 14 electrons. Copper has 29 electrons, 29 protons, and 35 neutrons. Valence The number of electrons in the outermost shell determines the valence of an atom. The outer shell is called the valence shell. Electrons contained in this shell are called tvalence electrons. An atom lacking only one or two electrons from its outer shell easily gains electrons to complete its shell, but a large amount of energy is required to free any of the electrons. An atom having a relatively small number of electrons in its outer shell in comparison to the number required to fill the shell easily loses its valence electrons. The maximum number of electrons that can exist in the valence shell is eight. CONDUCTORS, SEMICONDUCTORS, AND INSULATORS All elements may be placed into one of three categories: conductors, semiconductors, and insulators, depending on their ability to conduct an electric current. Conductors conduct electricity very regularly. Insulators have an extremely high resistance to the flow of electricity. All matter between these two extremes is called semiconductor. Normally, conductors have three or fewer valence electrons; insulators have five or more valence electrons; and semiconductors usually have four valence electrons. At room temperature copper contains a considerable amount of heat energy. Since heat energy is one method removing electrons from their orbits, copper contains many free electrons that can move from atom to atom. When not under the influence of an external source these electrons move about randomly. When controlled by an external fource, the electrons move generally in the same direction. The effect of the movement is felt almost instantly at the speed of light from one end of the conductor to the other, even though the electrons are traveling at a much slower speed. This movement is called an electric current. Silver, copper, gold and aluminum are material with few valence electrons that make good conductors. Conductors are usually in the form of wire. Insulators have few free electrons. Some examples are rubber, plastic, enamel, glass, and mica. There is no perfect insulator. Germanium and silicon are two common semiconductors used in solid-state devices. ELECTROSTATICS Static Electricity If electrons are removed from the atoms of a body of matter, there remain more protons than electrons and the whole body becomes electrically positive. When the positively charged body comes into contact with a body having a neutral charge or a negative charge electrons will from from the more negative body and enter the positive body. The flow continues until both sides are equal. The existence of the electrical force where current cannot flow is called static electricity. Ionization When the atom loses electrons or gains electrons it is said to be ionized. An atom having more than its normal amount of electrons acquires a negative charge and is called a negative ion. The atom that gives up some of its normal electrons is left with fewer negative charges than positive and is called a positive ion. Ionization is the process by which an atom loses or gains electrons. Nature of Charges There are always ions present in any material due to normal molecular activity. If either type of ion outnumbers the other in a particular material the material has a net positive or negative charge. In most solids the transfer of charges is by the movement of electrons rather than ions. The transfer of charges by ions becomes significan when one considers electrical activity in liquids or gases. Charged Bodies Like charges repel each other. Unlike charges attract each other. A positive charge and a negative charge move toward each other. COLUMB'S LAW OF CHARGES F= (kq1q1)/d**2 F = The force in newtons (N) Q1,q2 = the charges in coulombs © K = a contant (8.988 x 10**9) for converting the values to SI units D = the distance in meters between the charges A columb is equal to 6.25 x 10**18 electrons. The uC is often used. The importance of the equation is in the understanding that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance. Electric Fields The space between and around charged bodies in which their influence is felt is called an electric field of force. Click here to move back to the top of this page.
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